View Javadoc
1   /*
2    * Copyright 2014 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.handler.codec.compression;
17  
18  /**
19   * Random numbers for decompress Bzip2 blocks.
20   */
21  final class Bzip2Rand {
22      /**
23       * The Bzip2 specification originally included the optional addition of a slight pseudo-random
24       * perturbation to the input data, in order to work around the block sorting algorithm's non-
25       * optimal performance on some types of input. The current mainline bzip2 does not require this
26       * and will not create randomised blocks, but compatibility is still required for old data (and
27       * third party compressors that haven't caught up). When decompressing a randomised block, for
28       * each value N in this array, a 1 will be XOR'd onto the output of the Burrows-Wheeler
29       * transform stage after N bytes, then the next N taken from the following entry.
30       */
31      private static final int[] RNUMS = {
32              619, 720, 127, 481, 931, 816, 813, 233, 566, 247, 985, 724, 205, 454, 863, 491,
33              741, 242, 949, 214, 733, 859, 335, 708, 621, 574,  73, 654, 730, 472, 419, 436,
34              278, 496, 867, 210, 399, 680, 480,  51, 878, 465, 811, 169, 869, 675, 611, 697,
35              867, 561, 862, 687, 507, 283, 482, 129, 807, 591, 733, 623, 150, 238,  59, 379,
36              684, 877, 625, 169, 643, 105, 170, 607, 520, 932, 727, 476, 693, 425, 174, 647,
37               73, 122, 335, 530, 442, 853, 695, 249, 445, 515, 909, 545, 703, 919, 874, 474,
38              882, 500, 594, 612, 641, 801, 220, 162, 819, 984, 589, 513, 495, 799, 161, 604,
39              958, 533, 221, 400, 386, 867, 600, 782, 382, 596, 414, 171, 516, 375, 682, 485,
40              911, 276,  98, 553, 163, 354, 666, 933, 424, 341, 533, 870, 227, 730, 475, 186,
41              263, 647, 537, 686, 600, 224, 469,  68, 770, 919, 190, 373, 294, 822, 808, 206,
42              184, 943, 795, 384, 383, 461, 404, 758, 839, 887, 715,  67, 618, 276, 204, 918,
43              873, 777, 604, 560, 951, 160, 578, 722,  79, 804,  96, 409, 713, 940, 652, 934,
44              970, 447, 318, 353, 859, 672, 112, 785, 645, 863, 803, 350, 139,  93, 354,  99,
45              820, 908, 609, 772, 154, 274, 580, 184,  79, 626, 630, 742, 653, 282, 762, 623,
46              680,  81, 927, 626, 789, 125, 411, 521, 938, 300, 821,  78, 343, 175, 128, 250,
47              170, 774, 972, 275, 999, 639, 495,  78, 352, 126, 857, 956, 358, 619, 580, 124,
48              737, 594, 701, 612, 669, 112, 134, 694, 363, 992, 809, 743, 168, 974, 944, 375,
49              748,  52, 600, 747, 642, 182, 862,  81, 344, 805, 988, 739, 511, 655, 814, 334,
50              249, 515, 897, 955, 664, 981, 649, 113, 974, 459, 893, 228, 433, 837, 553, 268,
51              926, 240, 102, 654, 459,  51, 686, 754, 806, 760, 493, 403, 415, 394, 687, 700,
52              946, 670, 656, 610, 738, 392, 760, 799, 887, 653, 978, 321, 576, 617, 626, 502,
53              894, 679, 243, 440, 680, 879, 194, 572, 640, 724, 926,  56, 204, 700, 707, 151,
54              457, 449, 797, 195, 791, 558, 945, 679, 297,  59,  87, 824, 713, 663, 412, 693,
55              342, 606, 134, 108, 571, 364, 631, 212, 174, 643, 304, 329, 343,  97, 430, 751,
56              497, 314, 983, 374, 822, 928, 140, 206,  73, 263, 980, 736, 876, 478, 430, 305,
57              170, 514, 364, 692, 829,  82, 855, 953, 676, 246, 369, 970, 294, 750, 807, 827,
58              150, 790, 288, 923, 804, 378, 215, 828, 592, 281, 565, 555, 710,  82, 896, 831,
59              547, 261, 524, 462, 293, 465, 502,  56, 661, 821, 976, 991, 658, 869, 905, 758,
60              745, 193, 768, 550, 608, 933, 378, 286, 215, 979, 792, 961,  61, 688, 793, 644,
61              986, 403, 106, 366, 905, 644, 372, 567, 466, 434, 645, 210, 389, 550, 919, 135,
62              780, 773, 635, 389, 707, 100, 626, 958, 165, 504, 920, 176, 193, 713, 857, 265,
63              203,  50, 668, 108, 645, 990, 626, 197, 510, 357, 358, 850, 858, 364, 936, 638
64      };
65  
66      /**
67       * Return the random number at a specific index.
68       *
69       * @param i the index
70       * @return the random number
71       */
72      static int rNums(int i) {
73          return RNUMS[i];
74      }
75  
76      private Bzip2Rand() { }
77  }